1. Field of the Invention
The present invention relates to a magnetic tape reproducing apparatus for reproducing digital information such as music recorded on a magnetic tape.
2. Description of the Related Arts
An apparatus for digitally recording data onto a predetermined track of a magnetic tape has been put to practical use, which is known as, for example, an R-DAT (rotary digital audio tape recorder) system. This digital magnetic tape apparatus advantageously suffers less signal deterioration during recording or reproducing than the conventional analog recording system, and hence a variety of editing operations such as follow-up recordings, high-speed searches or selections of music using a sub-area as well as high-density recording can be easily performed. Accordingly, such a digital magnetic tape apparatus is applicable not only to audio recording, for example, in the R-DAT format described above, but also to recording or reproducing of graphics or other digital data.
In such a digital magnetic tape apparatus represented by the R-DAT, commonly employed is a so-called helical scan method in which a rotary head scans diagonally relative to a running magnetic tape as shown in FIGS. 7A and 7B. In the drawings, a magnetic tape 12 is transferred from a feed reel 14 to a take-up reel 15 while being in contact with a cylindrical rotary drum 102 at a lap angle of 90.degree.. The drum 102 has a rotational axis 105 which is slightly slanted with respect to the direction orthogonal to the tape running direction. A pair of magnetic heads 11, disposed on the circumferential surface of the rotary drum 102 diametrically opposite to each others are adapted to form linear elongated tracks on the magnetic tape 12 which are slightly inclined with respect to the tape running direction 107.
In the above-mentioned helical scan method, each of the tracks on the magnetic tape generally includes a tape format consisting of a PCM (main) area for digitally recording data and a sub-area for digitally recording sub-code signals representative of characteristics of the data, and is successively formed on the magnetic tape for the predetermined data recording.
FIG. 8 depicts tracks formed on the magnetic tape 12. As is apparent from this drawing, the tracks 114 are successively formed on the magnetic tape 12 so as to define an angle relative to the tape running direction T. Each of the tracks 114 includes a centrally provided PCM area 115, ATF (automatic track finding) areas 116 provided adjacently on both sides of the PCM area, and sub-areas 117 further provided adjacent on both sides of the ATF areas 116. Among them, the PCM area 115 acts as a region where main signals are recorded as music data, the ATF area 116 serves as a region where information required for tracking is recorded, and the sub-area 117 functions as a region where program numbers representing the music numbers, start code signals representing initiating positions of the above-mentioned main signals (hereinbelow, referred to as start ID's), priority code signals, reproducing time information and the like are recorded. Each of the music data (hereinafter, referred to simply as programs) is adapted to be controlled by sub-code signals of the sub-code areas provided on each of the tracks, and the program numbers are one after another written into the sub-areas of the required track between each of the segmented data. Then, the program number is searched to select the desired program. In cooperation with a program memory storing these recording orders, a random high-speed search is also available.
The start code signal is called a start ID, which is one of the most important sub-code signals. This start ID is usually recorded for nine seconds at the head of music data for use in the reproduction or high-speed search. By way of example, when this signal is detected in the ordinary reproduction mode, a start indication lamp provided on, for example, a console is turned on during that detection, to display that the head of music data is present.
In the magnetic tape reproducing apparatus such as the RDAT, the program search has been hitherto carried out in the following manner. As shown in FIG. 9, when the N-th program 108 is searched for by a high-speed forward search (hereinafter, referred to as FF), the magnetic tape is first transferred at a speed 200 times the ordinary tape running speed while the start ID is being hunted (Step S 921). In this case, the tape is often found at a position beyond the rise position of the target start ID 109 due to a high-speed of the tape relative to the speed of rotation of the rotary drum 102. This detection brings about a braking action onto the take-up reel 15, and feed reel 14 (FIG. 7), and the tape comes to a stop after the predetermined distance of running (step S 922). Then, the fall (rise in the FF direction) position of the start ID 109, in other words, leading edge of the start ID is hunted (Step S 923) while the tape is being rewound at a speed in the order of 10 times the ordinary reproduction speed.
Thus, in the conventional magnetic tape reproducing apparatus, when the program is searched for by the high-speed search, the tape is reversed and the detection of the leading edge of the start ID is initiated immediately after the stop of the tape due to the braking action following the detection of the start ID. However, at the time when the force of the brake brings the tape to a stop, the tape may become loose due to the lag in the timing between the stop of the feed reel 14 and the stop of the take-up reel 15, which leads to an unstable contact with respect to the rotary drum 102. If the rotation of the tape is reversed to look for the start ID immediately under such conditions, a pseudo signal looking like the fall (leading edge) of the the start ID is liable to be detected, which may be mistaken for a true program leading edge. This prevents the target music from being reproduced from the beginning, and instead the reproduction may be disadvantageously initiated halfway through.
Thus, an object of the present invention is to overcome the above problems.
The present invention was conceived in order to solve the above problems, and aims at providing a magnetic tape reproducing apparatus capable of accurately detecting the leading edge of the program for the reproduction, without any malfunction even during high-speed search.